The present invention relates to a pressure transmitter for sensing a physical variable related to a process fluid of an industrial plant having improved functions. More precisely, the present invention relates to a pressure transmitter that distinguishes itself from known types of pressure transmitter thanks to its higher versatility of use, which allows to obtain lower manufacturing and installation costs.
It is known that pressure transmitters are widely used in control systems of industrial processes with the aim of sensing/measuring one or more physical variables, such as absolute, relative or differential pressure, flow, turbulence, level and the like, of a process fluid and to send to a controller, by means of an appropriate communications network, for example a 4-20 mA communication line, signals that are representative of the value of the sensed physical variable. Typically, a pressure transmitter comprises a main body suitable to accommodate a pressure sensor and a plurality of electronic circuits. A pressure sensor is usually used which notoriously provides one or more measurements related to pressure (relative, differential or absolute pressure); by considering the appropriate boundary conditions, it is possible to obtain easily measurement values that also relate to other physical variables of the process fluid (level, flow, turbulence and the like) that it would be more difficult to transduce directly.
The electronic circuits are connected to the pressure sensor and process the signals supplied thereby so as to generate measurement signals that are representative of the process variable to be sensed. Said electronic circuits are furthermore given the task of managing the communication of the pressure transmitter with any external devices, for example with controllers or other pressure transmitters.
A pressure transmitter generally comprises an additional portion, which essentially consists of a process coupling system suitable to contain the process fluid so as to place the transmitter in contact with the process fluid, i.e. couple it, so that the transmitter can sense its intended physical variables.
Said process coupling system comprises a plurality of flanges, which are connected to manifold pipes inside which the process fluid flows. Each flange is rigidly associated with the main body of the pressure transmitter, at an interface surface provided with a flexible separation membrane. The separation membrane comprises an external wall, which is exposed to the process fluid, and an internal wall, which is coupled mechanically to the pressure sensor.
The mechanical coupling between the internal wall of each membrane and the pressure sensor is often obtained by means of a system of pipes filled with incompressible fluid, so that the pressure of the process fluid is transmitted without any damping effect.
However, known pressure transmitters have drawbacks.
A first drawback arises from the fact that the geometry of the process coupling system is generally rigidly preset. For example, in some known pressure transmitters, the coupling system has a co-planar geometry: the flanges are rigidly associated with interface surfaces that lie on a common horizontal plane, substantially at right angles to the main axis of symmetry of the pressure transmitter. As an alternative, in other known types of pressure transmitter the coupling system has a vertical geometry: in this case, the flanges are associated with interface surfaces arranged on vertical planes that are substantially parallel to the main axis of symmetry of the pressure transmitter.
Generally, in known types of pressure transmitter it is extremely difficult, if not impossible, to change the type of geometry of the coupling system, varying for example the arrangement of the flanges. Accordingly, since the manifold pipes are also in turn rigidly coupled, it is often necessary to resort, in order to obtain the connection of the flanges to the manifold pipes, to connection elements or to tanks arranged appropriately.
A second drawback arises from the fact that known types of pressure transmitter generally have a process coupling system that has a scarcely modular structure. This further reduces the possibility to connect the flanges to the pipes of manifolds easily and without the use of auxiliary elements.
Accordingly, one can say that known types of pressure transmitter generally have a relatively low operating flexibility. This fact implies that their installation and activation are sometimes difficult. This entails an increase in installation and operating costs. Furthermore, it is often necessary to resort to pressure transmitters of a different type in order to meet the different operating requirements that can occur during the installation of the control system. This clearly determines an increase in the production costs of the pressure transmitter.